Wrapping material



June 23, 1936- J. a. M NALLY ET AL 2,044,304

WRAPPING MATERIAL Filed June 17, 1932,

I I I, M I i p I g & 0 W I GumWzzcfi Cellulose Sieazale.

r I r I I I I 1 I 1 CelluldbeEslerBaseSIzeeh MmmEBemiM 11106 GM MZIy;gwuentozv,

Patented June 23, 1936 PATENT OFFICE WRAPPING MATERIAL James G. McNallyand Norman F. Beach, Rochester, N. Y., assignors to Eastman KodakCompany", Rochester, N. Y., a corporation of New York Application June17, 1932, Serial No. 617,808

8 Claims.

This invention relates to the manufacture of a thin, flexible,transparent, moisture-proof type of wrapping material, and moreparticularly to a cellulosic material having an overcoating on one orboth sides which renders the sheeting sub-- stantially impermeable tomoisture.

It is well known to coat paper,.cloth and various other types of fibrousand non-fibrous materials to render them resistant to the penetration ofwater and other liquids by applying a composition containing gums,waxes, oils and other ingredients. It has also been proposed towaterproof a sheet of regenerated cellulose by applying thereto acomposition containing a cellulose derivative base and variousingredients of a waterproofing character. The present invention is notconcerned broadly with waterproofing or moistureproofing, but relatesprimarily to the treatment of a particular type of base sheet byapplying thereto a new and improved moistureproofing composition which,not only cuts down the amount of moisture transmitted by the untreatedsheeting, but also renders it substantially impermeable to water andother liquids. The moistureproofing composition of the present inventionis of an extremely simple character,

readily formulated and easily applied.

The principal object of our invention is to provide a means of renderingthin sheets of cellulose acetate and similar colloidized organiccellulose ester and/or mixed ester material, such as cellulosepropionate, cellulose butyrate, cellulose stearate, cellulose acetatepropionate, cellulose acetate butyrate and the like, and even sheets ofregenerated cellulose material, waterproof and moistureproof. A furtherobject is to provide a wrapping material which is not only waterproofand moisture-proof, but also highly transparent, flexible, odorless andnon-tacky. A further object is to provide a water and moistureproofcoating composition suitable for application to thin cellulose acetatesheeting or similar materials which is simple to compound and apply andis distinguishedtfrom other known materials by inclusion of a specialcomponent. Other objects will hereinafter appear.

The above objects are accomplished by formulating a moistureprooflngcomposition in the manner hereinafter described and applying it to abase sheet of cellulose acetate or the like in such manner that anextremely thin moistureprises a mixture of gum, wax, and anotheringredient having special properties. We have found that if a mixedcellulose organic ester is employed in connection with gum and wax asthe third component, the ability of a sheet material, such as celluloseacetate coated. therewith to transmit moisture will be reduced to aremarkable degree. After conducting many experiments with a large numberof compositions of this general nature, we have found that compositionsof gum, wax and celluloseacetate stearate are particularly effective andgive rise to unexpected moisture-resisting qualities.

As examples of waxes which may be employed in our improvedmoistureproofing composition may be mentioned paraffin, ceresin,beeswax, pimela, lanolin, spermaceti, Montan,. bayberry, Japan,candelilla and Chinese wax, any of which may be used singly or incombination with one another, or with other waxes of this general na-'ture known to those skilled in the art.

The gums may be either natural or synthetic, typical examples of whichare ester gum, damar, rosin, gum mastic, cumar resin, sandarac, certainof the vinyl resins, and other artificial gums or resins. As in the caseof the waxes, these may also be used alone or in various combinations.

The mixed cellulose organic ester which we prefer to use with the gumsand waxes above referred to is cellulose acetate stearate. While we arenot limited to a cellulose acetate stearate of any particular stearylcontent, we prefer to use a compound of relatively high stearyl content.We have found, for example, that a cellulose acetate stearate containing10-40% stearyl is highly satisfactory, and a gum-wax compositioncontaining this particular compound when deposited upon a thin,transparent sheet of cellulose acetate decreases its moisturetransmitting propensities to a very marked extent. These mixed estersmay be prepared in accordance with the disclosure of the Clark and MalmPatent 1,800,860. Broadly speaking, the higher the stearyl content ofthe particular mixed ester used, the greater the amount of wax which maybe employed in the composition. As stated, 1040% stearyl is satisfactoryand 20-30% is probably optimum.

The proportions of the various ingredients used in the moistureproofingcomposition in accordance with the present invention may vary withinrather wide limits, but, as a general rule, we prefer to maintain thepercentage of mixed cellulose organic ester, such as cellulose acetatestearate, at about 20% based on the total solids, the gum and waxcomponents making up the balance of the solids in about equalproportions. The cellulose mixed ester content may run as high as 34%and even higher, as for instance approximately 50%, depending upon thecharacteristics desired in the finished material.

Our coating composition is particularly characterized in that we areable to incorporate in the composition a much higher percentage of waxthan it has heretofore been possible to in' corporate in amoisture-proofing composition with any other celluiosezderivative'. Forinstance, it is wellknown that moisture-proof, regenerated cellulosesheeting now extensively upon the market, is coated with amoisture-proofing composition containing a cellulose derivative such ascellulose nitrate, together with 15% of wax, based upon the weight ofthe totals'olids, as the upper limit of the wax content for the coatingcomposition. It is, therefore, most unusual to be able to incorporate inthe coating composition, quantities of wax amounting to as much as 40 or50% of the total weight of the solids contained in the composition or asmuch as 200% or more of wax based upon the weight of the cellulosederivative itself. Accordingly, our invention stands out as being thefirst coating composition to contain a cellulose derivative insubstantial amounts and a proportion of wax equivalent to one-third ormore of the total solids in the composition, or stated otherwise,equivalent to to 200% of the cellulose derivative contained in thecomposition, together with the desirable properties concomitant withhigh wax content.

The solid constituents above described are dissolved in a suitablesolvent, typical examples of which are toluene, xylene, benzene,ligroin, solvent naphtha, ethylene dichloride, trichlorethylene, andcarbon tetrachloride. The solvent is selected primarily upon the basisof its common solvent power for the gum, wax, and the cellulose acetatestearate. It should also be selected on the basis of its lack of solventpower for the material of the base sheet which is to be moistureproofed.As a general rule, the solvent should be of such a character that itwill not exert an undesirable softening or weakening action on the basesheet material. This is especially true when applying the hereindescribed coating compositions to thin, cellulose ester material of theorder of .001" in thickness. With thicker materials, say of the order of.005 inthickness, the solvent may have a slight softening or swellingaction on the base sheet which is not undesirable and in some cases mayactually assist in anchoring the moistureproof coating to the sheeting.

As indicated above, the base consists of a thin, flexible, transparentsheet of cellulose ester or material having similar properties. ForWrapping purposes, a sheet having a thickness of .001" is preferred,although material of varying thicknesses may be employed according tothe purpose to which the material is eventually to be put. Our inventionis not limited to the moistureproofing of cellulose ester material, asthe novel moistureproofing compositions herein described may be used forforming a moisture resistant coating over a variety of surfaces, such asthose of paper, cloth, wood, and other fibrous or non-fibroussubstances.

Our compositions may include, as an optional ingredient, a plasticizerfor the mixed cellulose ester, such as triphenyl phosphate, dimethylphthalate, and others, in' amounts'up to about 10% of the total weightof solids. Likewise, coloring materials, such as dyes, pigments, pearlessence, and the-like may be incorporated in the compositionsto'producevarying eflects."

In the following examples, we" have set forth several of the preferredmoistureproofing compositions of our invention, but it is to beunderstood that they are included merely for purposes of illustrationand not as a limitation 5 thereof.

Formula No. I

, Grams Cellulose acetat' eii"s tearat Paramn wax (melting poin Estergum 40 Dissolved in a mixture of 500 cc. of toluene and 250 cc. of ethylacetate.

Dissolved in a mixture of 500 cc. of toluene and 20 250 cc. of butylacetate.

A typical moistureproofing process and product in accordance with thepresent invention is illustrated in the accompanying drawing in 25which:

Fig. 1 is a diagrammatic representation of one form of apparatus forcarrying out the invention in which the base sheet is coated on bothsides simultaneously.

Fig. 2 is a cross section through a portion of the coated materialillustrating the structure of the finished product, the thickness of therespective portions being greatly exaggerated in the interest ofclearness of illustration.

Referring to the drawing in detail, the numeral l' designates a sheet ofthin cellulose acetate of about .001 in thickness which is fed fromsupply roll 2 over guide roll 3 into immersion vat 4 containing liquidmoistureproofing composition 5, such as that represented by Formula No.I above. The level of liquid in vat 4 is maintained at such a heightthat the composition flows into the V- shaped opening between thedown-coming and up-going portions of the sheeting and is therebysimultaneously applied to both sides of the sheet. During its passagethrough the vat 4, the sheet I passes under guide roll 6, up betweenadjustably mounted scraper bars 1 and 8 which serve to remove excesscoating fluid from its surfaces, thence through drying chamber 9 whereit is subjected to a drying current of air maintained at a temperatureranging from 50-100 C. As the sheet I emerges from the drying chamber 9it passes over drum [0 and thence to wind-up roll II.

Fig. 2 illustrates the structure of the finished product. The base sheetA comprises a thin sheet of cellulose ester material, having extremelythin coatings B on both surfaces. These coatings comprise a mixture ofgum, wax, and cellulose acetate stearate which substantially preventsthe penetration of moisture into or through the sheeting. Optionally,the coating material may be applied to one side of the sheet only bymeans of a subbing roll or equivalent-means well known to those skilledin the art.

It. is found that the material produced accordingto the presentinvention resists to a remarkable degree thetransmission of moisture.For 70 example, an untreated sheet of cellulose acetate may undercertain conditions transmit as much -as- 1.2 milligrams of moisture persquare centimeter per hour. The; improved product ,orthe presentinvention, underwhe, same conditions, 75

per square centiimportant.

Our invention is not confined to the production of moisture-proofsheeting, since the compositions typified by the formulae given abovemay be used for a variety of water-proofing or moisture-proofingoperations. So far as we are aware, we are the first to have suggestedthe use of a composition in which an extremely high degree ofmoistureproofing is obtained by the use of the cellulose mixed. organicesters in connection with gum, wax and other moistureproofing materials.

As is well known, a considerable amount of waste occurs in the ordinaryoperations of manufacturing coated sheeting and in its use as map pingand packaging material. This would represent a serious economic losswere it not for recovery processes in which the various ingredients ofthe sheeting can be reclaimed. The material of the present invention ischaracterized by the fact that it lends itself particularly well to suchrecovery processes. A simple and convenient method of reclaiming scrapderived from moistureproof sheeting of the type herein describedcomprises leaching the scrap with an organic solvent which may consist,for example, of toluene or benzene, which removes the moistureproofingcoating therefrom. The solvent is then drained off, the material dried,in which condition it may be reused in the production of furthersheeting, film or the like.

What we claim is:

1. An article of manufacture comprising a thin,

containing approximately 33% gum, 33% wax, and 34% cellulose acetatestearate.

2. A moistureproofing composition for cellulose acetate sheets or filmscontaining approximately 33% gum, 33% wax, and 34% cellulose acetatestearate dissolved in a solvent comprising about A; by volume ethylacetate and by volume toluene.

3. A moistureproofing composition for cellulose acetate sheets or filmscontaining cellulose acetate stearate and to 200% wax based upon theweight of cellulose acetate stearate.

4. A moistureproofing composition for cellulose acetate sheets or filmscontaining approximately 20-34% cellulose acetate stearate, 33-40% waxand the remainder gum.

5. A moistureproofing composition for cellulose organic ester sheetingcomprising a mixture containing at least 20% wax, at least an equalamount of cellulose acetate stearate, and the remainder gum.

6. An article of manufacture comprising a thin, flexible, transparentsheet of cellulose organic ester material adapted for wrapping purposescoated with a moisture-resistant composition comprising a mixturecontaining at least 20% wax, at least. an equal amount of celluloseacetate stearate, and the remainder gum.

7. An article of manufacture comprising a thin, flexible, transparentsheet of cellulose acetate adapted for wrapping purposes coated with amoistureresistant composition comprising cel-'

